1. Technical Field of the Invention
This invention most generally relates to methods and apparatus for drying coffee beans and other green crops or coarse granular bulk materials composed of beans, seeds, pods, or grains of relatively large and uniform size, to reduce the moisture content. More particularly, it relates to bulk product containers for use in low pressure airflow drying systems, including convective air and solar powered systems.
2. Background
The art of harvesting and processing coffee beans from tree-borne cherries to the green coffee bean of commerce consists of two principle methods, the xe2x80x9cdryxe2x80x9d method and the xe2x80x9cwetxe2x80x9d method. Either method must result in moisture content equivalent to one third or more of the bean""s weight being removed, to produce a commercial product.
The dry method is the more ancient and rudimentary. The cherries are hand-picked all in one picking, washed, and sun-dried on drying ground or concrete slabs in thin layers, usually for a period of two to three weeks. The beans are heated by solar radiation from above and by secondary radiation from the already warmed concrete slab below, while natural circulation of relatively dry air over the top of the beans slowly leaches out the moisture. The beans ferment during the process, and are turned several times a day to promote even drying. They are covered at night to protect them from reabsorbing moisture during the night time dewpoint and temperature changes.
In the wet method, only the ripe cherries are picked in any one picking of a tree. It may take three to five sequential pickings in a season over the time it takes between the earliest and the latest cherries to ripen. After the cherries are washed, the outside fruit pulp is removed by machines and the berries are then placed into large concrete tanks to ferment for twelve to twenty-four hours, then poured into concrete sluiceways or washing machines to be thoroughly washed in constantly running water. Then they are dried in much the same way as in the dry method, except that the drying time is shorter. These beans are then processed through hulling machines to remove the remaining layers of skin.
Problems with either method of this art include the inefficient, labor-intensive and lengthy sun-drying time of beans arranged on open air slabs. There have been introduced over the years, other manual, passive solar methods and devices attempting to promote and control air movement in combination with heat, to remove the moisture from bulk crops. Most typically, the beans or other materials being dried, are supported on a foramenous surface or in a container having at least foramenous bottom surface or screen, to permit a greater degree of circulation or air flow in contact with the underside as well as the topside of the bulk materials.
Various electrical powered and/or fuel-fired dryer systems have also been used to try to accelerate the drying time and prevent mold problems. There are many patents that describe related technologies and devices. Most of these alternatives add expense and complexity to an otherwise simple process. Failing to safeguard the beans from excess moisture, in particular the formation of mold during the drying process is crucial as the value of the crop drops dramatically if mold occurs. Over drying can also occur using accelerated methods; this also affects the quality and value of the crop. A sampling of the art of convective and low pressure air drying systems is included to provide context for the reader:
Stokes"" U.S. Pat. No. 4,490,926 (1985) discloses a solar drying device and method for lumber, tobacco and grain. It includes a solar collector, a drying chamber, and a dehumidification system. The background section mentions solar heated kilns and dryers with easy access and containerized methods, wheeled vehicles or carts, for moving materials into and out of the dryer. Insulation and double glazing of light-admitting sheet materials is discussed, as is passing air between a drying chamber and a dehumidifying chamber. The focus is on drying and reusing the air.
Sutherland""s U.S. Pat. No. 5,584,127 (1996) is a recent patent for a solar powered fruit dryer. The focus of the apparatus design is on re-circulation of a portion of the drying gas. It refers to air circulating through perforated shelves (col. 4, line 32) upon which the materials are arranged. Column 4, line 60, describes the physical embodiment in some detail, including air flow volumes.
Andrassy""s U.S. Pat. No. 5,001,846 (1991) is a solar drying apparatus with a translucent sloping top and means for evacuating the condensation from the moist air. The specification describes a perforated or porous tray on which the materials are arranged for drying. A solar powered fan forces drying air vertically through the porous tray.
Mullin""s U.S. Pat. No. 4,099,338 (1978) shows an elaborate, solar-assisted dryer for tobacco, onions, titanium dioxide drying, polyester fiber setting, and roasting nuts and cereals. The focus appears to be on ratios of solar heated makeup air in the circulation system to save fuel. The material is dried on a forarnenous conveyor belt.
O""Hare""s U.S. Pat. No. 4,501,074 (1985) is a convection powered solar food dryer that discloses a solar collector on the inlet side for heating intake air, and a vertical solar tower or column to accelerate the convection of warm air through the system by suction. The actual drying chamber can be remoted from the solar devices at each end of the convection system. The materials are arranged on shelves in the drying chamber.
Steffen""s U.S. Pat. No. 4,045,880 (1977) is a solar grain drying apparatus. It discloses a fan forced down draft eve inlet solar roof heating system, that then drives the drying air up through the perforated floor of the central drying chamber. The air is then exhausted upwards roof exhaust fans in the drying chamber ceiling.
Muller""s U.S. Pat. No. 1,556,865 (1923) is a solar powered dryer system for vegetable matter, consisting of a series of circumfrential racks with inlet perforations in the sidewalls and internal shelf brackets in the corners for holding drying shelves or trays. The racks are configured for interlocked stacking underneath a solar collector roof which has a central exhaust vent.
Pietraschke""s U.S. Pat. No. 4,391,046 (1983) is a solar heated grain drying system featuring an inlet manifold receiving multiple collector pipes and a fan blowing the intake air up through a perforated floor in the drying chamber.
Sweeny""s U.S. Pat. No. 278,199 (1883) is a coffee roaster showing perforated drums for containing the coffee beans, configured to revolve within a heated chamber. The drums are feed by hoppers through the ends. The drums use internal vanes to distribute the beans or other materials lengthwise, particularly for loading and unloading the drums. Heating is by other than solar means.
Danford""s U.S. Pat. No. 4,263,721 (1981) is a tobacco curing and drying structure that is configured for adding makeup air, using a heat exchanger and means for partial re-circulation.
It is useful, in conclusion, to review key aspects of the drying process. In the passive solar drying of bulk crops such as coffee and grain, airflow is generally more limited than heat, due to the relatively low differential pressure that can be generated in low cost, solar radiation dryers. It takes many hours or days to affect a significant reduction in moisture levels in the passive solar drying of crops. The relative amount of airflow to which the crops are directly exposed has been demonstrated in passive solar dryers to be the more significant factor to the dryer""s utility and efficiency, compared to simply adding more heat. Too much heat at this stage will do more damage than good.
A more deceptive aspect of the drying process is evident in commercial operations. Where a large quantity of the bulk crop is arranged as a deep layer on a screened floor of a container or drying room, and large volumes of air are forced up through the layer of loose material by fans, there is a distinct and inevitable lack of uniformity of the drying throughout the volume of the batch. Unequal rates of drying means that some percentage of the material is either over-dried, or still not dry, when the drying operation is concluded. Other modes of drying loose batches of bulk crops are all affected by this problem to some degree. This significantly affects quality.
It should be readily apparent from the above material that there are numerous and interrelated shortcomings in the art of basic dryers for bulk crops such as coffee; particularly as to the need for affordable advances in the state of the art for faster and more efficient drying without the need for substantially more complex or expensive equipment.
It is therefore an object of the invention to configure a container or dryer to obtain a more effective application of airflow, preferably a relatively dry, warm airflow, to the batch of bulk crops being subjected to the drying operation, while retaining a low cost structure and a simple bulk container handling system.
The invention in it""s simplest form is a low pressure airflow dryer or dehydrator system for granular bulk crops such as whole coffee beans, coca beans, and various grains where a substantial degree of moisture must be removed from the green beans, seeds, pods or grains, as part of the processing of the bulk product, in order to prepare it for further processing or use. The system, or key components, may be fabricated of stainless steel or plastic or such other materials as the user may find suitable for practical or regulatory reasons.
At the core of the system, there is a specialized bulk crop container specially configured to form a system of open wall airways uniformly distributed throughout the selected bulk material when it is added to the container, the airways connecting through openings in the top and bottom or sides of the container to airflow sources so that a distributed airflow can be directed through the airway network of the container to leach excess moisture efficiently from the bulk material.
The key to creating an open-wall airway network distributed throughout the container is the use of an internal structural network of minimal volume that provides an array of open face grooves or channels for airflow. The width of the face or top edge of each groove or channel is specified to be sufficiently narrow to prevent more than partial penetration of the groove by an average size coffee bean, particle of grain or kernel of the material being dried. The depth of the groove or channel is sufficient to assure an airflow passageway will remain open the full length of the groove or channel, when the container is full of the bulk material.
As explained, each groove or channel has an xe2x80x9copenxe2x80x9d or exposed side presented to the bulk material, but is sufficiently narrow to restrain the beans or kernels from filling the groove. This array of airflow channels provides a significant amount of the bulk material with direct or near direct exposure to the drying effects of the airflow in the groove or channel. Closely adjacent channels and uniformly spaced internal structural elements assures a relatively quick penetration of the drying effects of the airflow through the full volume of the bulk material in the container.
An efficient form of the required internal structure is a series of parallel partitions or airflow plates, dividing the container into very thin bays or compartments. The opposing faces of each partition present a parallel set of grooves to their respective bays or compartments, the grooves running the full height or width of the partition, and terminating at or actually projecting through a foramenous end wall or bottom panel such that the airway formed by the channel is accessible to an airflow that is ducted or channeled to that wall or bottom panel.
Practical embodiments of partition material for airflow plates, as will be discussed more fully below, include both ribbed panels, where both sides of a flat sheet are configured with parallel sets of raised ribs, the spaces in between which are channels; and corrugated panels, where both sides of the panel present to their respective bays, a parallel array of ridges and channels. The material may be extruded with the requisite ribs and channels, or formed from sheet stock. Other forms and embodiments of the internal structure are within the scope of the invention, and many have been disclosed by this applicant in priority documents.
The cycle of loading and unloading of the bulk product into and out of the dryer system may be enhanced by configuring the container or containers with bottom panel gates which can be opened to dump the contents, and closed for refill and operation of the dryer, without removing the container from the system. The container is scaleable and adaptable to dryer systems utilizing heat exchangers, solar radiation or other power sources for generating a warm, relatively dry, low to moderate pressure airflow. The container, inserted or connected to the airflow plenum of the system for both inlet and exhaust, absorbs the full flow of drying air through its interior.
By arrangement of the partitions, the airflow in the containers can be vertical, which is particularly useful for very low airflow pressure systems such as passive solar systems, where thermally generated convective airflow with minimal head pressure can be applied to a single level container. Alternatively, a user may, by using forced airflow systems able to provide a much greater pressure and volume of air than typical passive solar systems, with or without a supplemental heat source for adding more heat to the air, select or configure a dryer differently. The user may obtain either faster drying time of a small batch of materials by pushing more air through the dryer, up to a maximum useful rate of extraction of moisture; or greater batch capacity by using larger and more complex containers with either vertical or horizontal airflow networks, interconnected with ductwork to link the containers.
The top of the container must be fully open or openable so that bulk materials can be readily poured into all compartments of the container. Provisions for supporting the partitions or airflow plates within the container can be varied, and may depend on the orientation of the plates as whether vertical or horizontal, but the top edges of the partitions should be of somewhat uniform height and not be unduly restrictive to the loading or pouring in and leveling of the bulk materials. Gates or doors on the bottom of the container must resist the force and hold the weight of the bulk materials when loaded, and be readily openable so as to allow the dried bulk material to be emptied from each compartment or bay through the bottom of the container and collected for repackaging or further processing according to the user""s particular setup.
The rib and channel structure of the airflow plates provides an inherent resistance to bending of the plate lengthwise of the grooves and substantially less resistance to bending as between adjacent channels. Horizontally oriented airflow plates are generally able to be end supported by slots on the side of the container, while vertically oriented airflow plates may need intermediate supports. One form of intermediate support may be a sheet of material such as stainless steel, that is V-folded and then slotted at regular intervals from the fold to nearly the opposing edges. The V brackets are then inverted, oriented to span the container from side to side, spaced apart uniformly from each other and the ends of the container and secured to the sides, effectively dividing the container into bays. The airflow plates are then inserted into the slots so as to span the container at right angles to the V brackets, subdividing the bays into compartments.
The principle functional components of a dryer system of the invention, an airflow source, a bulk materials container configured to provide the uniformly distributed open wall airways network of the invention, a means for receiving and supporting the removable container within the dryer system in such a way as to constrain the air flow to flowing through the airways of the container, and means by which the container can be filled and emptied.
Still other objects and advantages of the invention will become readily apparent to those skilled in this art from the following detailed description, wherein I have shown and described only preferred embodiments of the invention, simply by way of illustration of the best mode contemplated by me on carrying out my invention.